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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc. |
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6th Feb 2018, 1:16 pm | #41 |
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Re: First Vintage TV - 1961 Perdio Portarama
you see the one on the extreme left offered in surplus adverts in Practical Television etc, it might have been mentioned before.
If anyone's interested, and if it hasn't been done before, I could scan the Which? article that reviews the portarama.
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7th Feb 2018, 1:27 am | #42 |
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Re: First Vintage TV - 1961 Perdio Portarama
Dismantled one the Portoramas this evening. I can confirm that transistor X112 is a Mullard OC81, as are X111 and X113.
Tomorrow I might attempt to fire up the set. Get it working and then it'll be possible to take oscilloscope traces from the frame timebase. DFWB. |
7th Feb 2018, 10:02 am | #43 |
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Re: First Vintage TV - 1961 Perdio Portarama
Interesting, the reversible or presumably bipolar electrolytics. When you do you recordings it would be interesting to see if during the frame scanning cycle they do get exposed to both polarities of applied voltage, or not.
I find with positive ground circuitry, it is easier to understand (for me at least) if I re-draw the circuit with complimentary transistors, reverse any diodes and make it negative ground, then it is less of a headache to figure out its function. |
7th Feb 2018, 9:19 pm | #44 |
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Re: First Vintage TV - 1961 Perdio Portarama
Performed some tests on the frame timebase.
The set was supplied with 11 volts from a bench power supply. Base connection to the line output transistor disconnected. The waveform across the frame oscillator ramp forming capacitors C129 and C130 is 1 volt P - P. The first attachment shows the waveform at the collectors of oscillator X111 and limiter X112. The second is the waveform present at the collector of the frame output transistor X114. (OC28) After the tests on the frame timebase were successfully carried out the base drive to the line output transistor was reconnected. The over current trip of the PSU was activated, >3amp so it's possible there is a fault in the line output stage. DY86 EHT rectifier anode cap removed but no change. The third attachment shows the circuit of the frame timebase of the Pye TT1. Note there is no buffer stage between the frame oscillator V25 and the driver transistor V26. Oscillator transistor V25 discharges the ramp forming capacitors C74 and C75 and initiates the frame flyback. DFWB. Last edited by FERNSEH; 7th Feb 2018 at 9:34 pm. |
8th Feb 2018, 1:55 am | #45 | |
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Re: First Vintage TV - 1961 Perdio Portarama
Quote:
This means that X112 is not being used as a "transistor" it appears, as its base-emitter junction is reverse biased at the time of flyback, but its base-collector junction is forward biased, simply being used as a diode, to discharge the sawtooth forming capacitors via the B-E junction of X113. Seems like an odd way to do it since the discharge current via X111 to ground would largely get sourced from X113's collector and emitter current, not X113's base current, which would be a fraction of that to discharge the capacitors. Maybe it was done to lengthen the frame flyback time to the correct value so that the discharge of the sawtooth forming caps was not too abrupt. Also, due to the nature of a bjt, it might actually still work reversing the E & C of X112 |
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8th Feb 2018, 3:57 pm | #46 |
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Re: First Vintage TV - 1961 Perdio Portarama
I used to work on these when they were new. Many a visit to Perdio for parts!
I agree with all those that urge to proceed with great caution. The line output stage was somewhat unreliable from the start, I remember suggesting that some sort of spring-loaded device to automatically replace the line o/p transistor might be devised! This didn't go down too well at Perdio... But then I had been previously told by a senior lecturer at tech college - "Don't worry about transistors in TV sets, they'll never be used, they can't stand the high voltage" I often wonder what happened to him... David. Last edited by Vintage Engr; 8th Feb 2018 at 3:59 pm. Reason: Typos. |
8th Feb 2018, 10:15 pm | #47 | |
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Re: First Vintage TV - 1961 Perdio Portarama
Quote:
The closest European pair to these specs are the AU103 & AY102. RCA's vertical output companion to the 2N3731 was the 2N3730, 200V rated. |
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8th Feb 2018, 11:13 pm | #48 |
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Re: First Vintage TV - 1961 Perdio Portarama
Argus25 wrote: "The closest European pair to these specs are the AU103 & AY102."
The AU103 is still available from online suppliers. Last year for the Pye TT1 I bought two AU103s from a components supplier in the Netherlands. Used as replacements for the 2G221 line output transistors. Made some progress with the Perdio Portorama today. I was convinced that the line output stage was OK but before powering the set from the mains I carried out tests on the power supply in accordance to the manufactures instructions. 1 - Remove fuses F3 and F4 and connect a 10ohm 10watt resistor between the junction of F3 and F4 and chassis. 2 - Connect a model 8 Avometer switched to it's 25V range, and an oscilloscope across the 10ohm resistor. 3 - Connect the receiver to the mains supply, depress button M and adujst VR406 for a reading of-11.6V on the meter. Adjust VR405 for minimum indication on the oscilloscope. Depress button O and disconnect the Avometer and oscilloscope. The power supply was confirmed to be working correctly and is delivering 11.6Volts across the 10ohm resistor, 100Hz ripple is 10mV. Replaced the fuses but still operating the set without drive to the line output transistor. Finally, the line drive is reconnected. Results can be seen in the attachment. DFWB. |
9th Feb 2018, 1:53 am | #49 |
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Re: First Vintage TV - 1961 Perdio Portarama
News Flash! Got pictures and sound. Just the frame timebase to sort out now.
DFWB. |
9th Feb 2018, 9:45 am | #50 |
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Re: First Vintage TV - 1961 Perdio Portarama
Looks good David! I think this is where mine entered the arena.
As soon as I get some junk cleared off the bench I will have a go at this one. John. |
10th Feb 2018, 11:49 am | #51 |
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Re: First Vintage TV - 1961 Perdio Portarama
The first oscilloscope trace shows a perfectly linear sawtooth waveform, so it could be said this is the ideal shape to drive the output transistor.
Well, in fact because of the non linear characteristics in the frame output stage a degree of pre-distortion is required, see second attachment. To keep the story short the linearity control VR101 was found to be faulty. Pre-distortion: this was the term used by Kolster-Brandes for the method of correcting the linearity of the frame scanning in many of the companies' early TV receivers. The shape of the sawtooth waveform was altered before applying it to the grid of the frame output valve. DFWB. |
10th Feb 2018, 12:19 pm | #52 |
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Re: First Vintage TV - 1961 Perdio Portarama
Aaah .... was this the malady that Gerry Wells christened 'KB Shoulder' i.e. whereat McDonald Hobley [or another poor announcer] developed a two foot long left or [usually] right shoulder? !!!!
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10th Feb 2018, 12:22 pm | #53 |
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Re: First Vintage TV - 1961 Perdio Portarama
Apart from the shape of the drive waveform, assuming it is correct, the most difficult part of the V scan for these early transistor TV's is near the end of the frame scan where the frame coil current needs to reach a satisfactory peak value.The screen image shows the typical problem with compression near the end of V scan.
To get good linearity there, near the end of the scan, it requires that that yoke coupling electrolytic is in perfect order with a low ESR and that the output transistor junction is in good shape and the drive waveform correct. Often as the V output transistor ages it cannot conduct adequately even with the original drive voltage waveshape being correct. One good test for the output transistor is to set the height control too high, if the raster can be deflected well over the lower CRT edge with increased setting of the height control, the transistor is probably good, so the next thing is to check the output electrolytic and then the drive waveshape/linearity circuit. |
10th Feb 2018, 4:45 pm | #54 |
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Re: First Vintage TV - 1961 Perdio Portarama
R140 (5.6Kohms) is in series with the height control, replacing it has increased the height and improved the frame linearity.
The other Perdio Portarama. The cabinet is in much better condition than the first set to receive attention. However, whereas there was no evidence of any service ever been carried out in that set the Portarama now on the bench shows plenty evidence of service work, and some of the work done is rather crude. Looks like the AF118 video amplifier transistor has been replaced with a silicon pnp BF421. Info: https://www.radiomuseum.org/tubes/tube_bf421.html I'll perform the same test procedures as were carried out to the other Portorama. First task is to test the receiver circuits by supplying 11volts from the bench power supplier. Drive to the line output transistor disconnected. Will report back my findings later today. Noteworthy is the special silver-cadmium battery that was made for this set. DFWB. |
10th Feb 2018, 5:56 pm | #55 |
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Re: First Vintage TV - 1961 Perdio Portarama
11 volts from the bench power supply is connected to the signals and frame timebase board. Favourable results, loud hiss from the loudspeaker so at least we know the sound circuits and tuner are in order. Sawtooth waveform present across the capacitors C129 and C130. The frame output stage can be assumed to be in order because a sawtooth of 7 volts and a flyback pulse measuring -20volts is present on the collector of the output transistor.
Now to move on to testing the power supply using the method discussed in post No.48. The 10ohm 10watt resistor used for test purposes is the component used to replace the unreliable and destructive component that was used in the BRC 3500 convergence board. DFWB. |
10th Feb 2018, 10:41 pm | #56 |
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Re: First Vintage TV - 1961 Perdio Portarama
Using the Perdio service manual test procedure the power supply was found to be in working order. Output voltage at the junction of Fuses FS3 and 4 is 11.50V. AC ripple is slightly higher than the other set @ 200mV P - P. However, I'm going to put the second Portarama aside because there is a fault in the line output stage. It might simply be a failed AU101 line output transistor or something more serious. Fuse FS3 blows on switch-on and does so with or without line drive to the AU101.
Strange that the fuse held up when the set was powered from the bench power supply. The other Portarama is working well except for some disturbance to the picture when the full RF output from the Aurora is supplied to the receiver. Attenuated signals cause no disturbance to the picture. It's likely to be the electrolytics in the vision AGC circuit have gone low capacity, C116 and C406. DFWB. Last edited by FERNSEH; 10th Feb 2018 at 10:49 pm. |
11th Feb 2018, 10:36 am | #57 |
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Re: First Vintage TV - 1961 Perdio Portarama
The frame linearity problem on mine was the 100 ohm frame lin pot itself being O/C. I used a neat convergence type pot that fitted exactly into the existing circuit board holes.
A few adjustments and it appears to be OK. There is a line 'twitch' at odd intervals that may be due to the preset hold control. I have cleaned it but I have had similar problems before that have turned out to be the control itself. It is shown working on the mains but is identical when working from the bench power supply. I will investigate the line problem when Spring arrives.. Regards, John. Last edited by Heatercathodeshort; 11th Feb 2018 at 10:42 am. |